In a liquid sealed vibration isolating device of this kind, when an extraordinary excessive amplitude vibration is inputted, there may be cases where negative pressure is developed instantaneously within a primary liquid chamber, and then, there is produced cavitation by which a part of hydraulic liquid bubbles. Since this cavitation involves generation of a considerable noise, it is required to prevent this noise, and there are proposed various kinds of constructions for noise prevention.
As one of them, there is proposed the construction that has a movable diaphragm section which is provided in a part of a partition member, and a circular arc shaped relief valve which is integrally provided in an outer peripheral portion of the movable diaphragm section. In this construction, when a normal vibration (a vibration within a range that is assumed at the time of normal traveling and the like) is inputted, a leak passage provided in the partition member is closed, and when an extraordinary vibration is inputted, the relief valve is opened so that a large amount of the hydraulic liquid is leaked from a secondary liquid chamber to a primary liquid chamber (see a patent reference 1).
Herein, the extraordinary vibration is an excessive amplitude vibration such as to produce the cavitation, and is the vibration which is not produced ordinarily at the time of the normal traveling and the like.